Sunscreen compositions are applied to the skin to protect the skin from the sun's ultraviolet rays that can lead to erythema, a reddening of the skin also known as sunburn. Sunlight or ultraviolet radiation in the UV-B range has a wavelength of 290 nm to 320 nm and is known to be the primary cause of sunburn. Ultraviolet rays at a wavelength of 320 nm to 400 nm, known as UV-A radiation, produce tanning of the skin. However, in the process of doing so, the UV-A rays can damage or harm the skin.
The photoprotection of keratinous substrates, especially skin, is considered by many to be necessary in order to facilitate protection from sunburn and photo-aging, as well as to decrease the chances of skin cancer development. There are typically two types of UV sunscreens used to accomplish photoprotection, namely, inorganic UV filters and organic UV filters.
Inorganic UV filters, such as titanium dioxide and zinc oxide, are typically employed in large quantities in order to ensure proper coverage/maximum protection over the surface onto which they are applied. As a result, they have a tendency to feel dry and impart an undesirable white color onto the treated surface.
While it is desirable to utilize organic UV filters, the incorporation of liposoluble UV filters into emulsion-type compositions has posed various stability challenges. This has been especially true when the desire was to incorporate larger amounts of said ingredients into compositions. Examples of lack of stability include discoloration of the formula and/or precipitation of the ingredients out of the composition. The problem, however, is that such organic filters, due to their electrolytic properties, are difficult to formulate with when it comes to long-term stability. This lack of stability oftentimes manifests itself in the form of re-crystallization of the filters in the composition, causing them to separate from the emulsion. Liposoluble UV filters present a challenge for incorporation into emulsions intended for topical application onto a keratinous substrate, as most traditional emulsions are thickened and/or stabilized with natural or synthetic polymers, such as gums and polyacrylates, which are very sensitive to electrolytes.
It is therefore an object of the present invention to provide a composition capable of stably carrying liposoluble UV filters, which is also tactilely pleasing to consumers upon application.